Into every generation a defining show is born. This happened on March 10, 1997 when Buffy the Vampire Slayer premiered. Yep, Buffy's 20 years old. Joss Whedon's little series that could starred Sarah Michelle Gellar as the titular slayer and amassed legions of fans during its seven-season run—and that fanbase is still growing thanks to streaming, reruns and comic books. The show's impact isn't lost on the fans, nor on the people behind the fan-favorite series.

Gellar took to Instagram to pay tribute to Buffy Summers and the series on the 20th anniversary of the show's premiere.

"20 years ago today, I had the greatest privilege to bring Buffy to your TV screens for the first time. It was a long and challenging road to get there. First the movie, then a passed over pilot presentation, and eventually a midseason time slot on a little known network," Gellar wrote.

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"That first season, we liked to think of ourselves as the little show that could. While we knew the potential, I don't think any of us saw the lasting impact our show would have. As an actor, you wish for that one role where you can leave your mark and forever be remembered, with Buffy I got so much more. She's a feminist challenge to gender hierarchy. Buffy may have been the Chosen One, but I was the lucky one," she continued.

In her post, Gellar thanked executive producer Gail Berman, the crew, Whedon "for trusting me to give life to one of the greatest female characters ever created" and her various costars including James Marsters, David Boreanaz, Michelle Trachtenberg and Alyson Hannigan.

"And lastly, but most importantly thank you to all of you, the fans," she said. "We made this show for you, and your unwavering support has kept this show going long past our seven years. You are everything. And always remember...'if the apocalypse comes, beep me' #buffyslays20"

Hannigan, Buffy's best friend the witchy Willow Rosenberg on BtVS, thanked international fans first and tweeted, "Thank you for all the International #20YearsOfBuffy love!!! Does this means I can start eating cake now as long as it's Australian cake?"

She followed up with another Twitter tribute: "Wow. #20YearsOfBuffy @joss What can I possibly say to thank you? No really, what can I say?!? I need YOU to write it!!!" Whedon responded to Hannigan, retweeting her and adding heart emojis and: "And I need you to say it."

Nicholas Brendon, Xander Harris on the series, tweeted to fans: "20 years ago the world changed. My life changed . What a beautiful ride it was and always will be. Thank you Lovlies ! #buffyslays20 #BTVS."

James Marsters, the vampire Spike, also took to Twitter, but added a selfie. See above.

Charisma Carpenter, Cordelia, posted a lengthy note on her Instagram, thanking the producers, crew and of course, the fans. "What an honor to have been a part of something that resonated so deeply with so many and is equally relevant today as it was then," she said. "It's impossible to articulate."

Meanwhile, Buffy's Watcher Giles also chimed in.

"#BuffySlays20 Here's to all who watched, and all who were part of its creation, but most of all, here's to you @joss - grrrr,aargh x," Anthony Stewart Headtweeted out, referencing Whedon's company Mutant Enemy's slate.

Julie Benz, Darla on Buffy and Angel, tweeted her thanks to Whedon with a GIF of her character. "20yrs ago @joss gave me a chance to be a small part of something big! I'm eternally grateful! #buffyslays20," she wrote. Emma Caulfield, Anya the ex-vengeance demon on Buffy, also shared her thoughts on Twitter.

"A huge thank you for a gift that changed my life forever. Love to all the cast, the writers, the crew &the show's captain J! #BuffySlays20," she wrote.